MSN Search Going Solo With adCenter Ads; Dropping Yahoo Ads?

There is some speculation over at Search Engine Watch Forums that MSN has dropped Yahoo! Search Marketing ads completely for its own ads, MSN adCenter. jbgilbert in the thread notes that he has yet to see a YSM ad on MSN since May 1st.

He asks if this is for real or a temporary glitch. It is unlikely that MSN would switch over 100% to their ad network, prior to leaving beta.